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Applicability and limitations of redundancy cal. in phased array stations

Applicability and limitations of redundancy cal. in phased array stations. Parisa Noorishad, Stefan Wijnholds, Arnold van Ardenne & Thijs van der Hulst YERAC2011, Manchester, 18 th -20 th July. 2011. A few words about new radio telescopes. Introduction & Motivation. Introduction:.

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Applicability and limitations of redundancy cal. in phased array stations

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  1. Applicability and limitations of redundancy cal. in phased array stations Parisa Noorishad, Stefan Wijnholds, Arnold van Ardenne & Thijs van der Hulst YERAC2011, Manchester, 18th -20th July. 2011

  2. A few words about new radio telescopes

  3. Introduction & Motivation

  4. Introduction: • [1] J. E. Noordam & A. G. de Bruyn, Nature, 14 oct. 1982 • [2] M. Wieringa, PhD thesis, Leiden Univ., 1991

  5. Introduction:

  6. Why redundancy? • Independent of a sky model, • Less sensitive to RFIs, • Computationally cheap and fast, • Simple to implement (important for SKA), • Could also be used as a diagnostic tool. • Regularity in a station configuration e.g. in MWA, HBA, EMBRACE.

  7. Redundancy in HBAs Introduction & Motivation

  8. Beam identicalness: CAESAR: Computationally Advanced and Efficient Simulator for Arrays [Rob Maaskant et al.]

  9. When redundancy fails:

  10. When redundancy holds:

  11. Checking the influence of non-identical sidelobes

  12. The systematic error due to non-identical sidelobes

  13. Quantifying that systematic error: The potential calibrator sources for RS208, on 24th of Nov. 2009 at 21:29:04 UTC and the systematic errors in the amplitudes and the phases of the redundant visibility due to the contribution of other strong sources through non-identical sidelobes.

  14. The plots of the residuals for corrected redundant visibilities

  15. Redundancy cal. Quality Introduction & Motivation

  16. CRB and the actual variance of the estimated parameters: We tracked CasA on 24th November 2009 from 15:25:43 UTC until 22:12:19 UTC.

  17. Redundancy cal. Limitations Introduction & Motivation

  18. Limitations of the redundancy calibration method: • Station configuration • Mutual coupling between the station elements which leads to: • Non-identical beams of the station elements • Presence of baseline dependent noise • SNR of the observed sky

  19. Station configuration and the condition of redundancy calibration

  20. One more point

  21. Model based cal. method: • The mutual coupling seems to be a non-dismissible effect (for phased array stations). • We need beam model of each individual station elements e.g. each tile at HBAs. [1] Wijnholds & van der Veen, 2009 [2] Wijnholds & van der Veen, 2010

  22. Summary & Conclusion

  23. Summary: • Applicability and limitations of the redundancy cal. for phased array station was investigated. • Conclusions: • Redundancy cal. is a stand-alone gain cal. method. • Using redundancy requires taking into account the parameters which affects its applicability and performance. • Identical beam; Mutual coupling seems to be a non-dismissible effect, no matter which method we use. • Next Step: • To do more rigorous CRB and Monte-Carlo analysis for two existing implementations of the redundancy method. • To evaluate the merit of the redundancy in UVW-space at the whole array level using SKA configuration.

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